A 31-year-old man remains in hospital tonight after almost drowning at the Walter Baker Sports Center, Tuesday night.

It appears he was attempting a rare sport known as free-diving. Free-divers train to spend several minutes underwater without access to an air supply.

Paramedics say that's what a man was doing at the Walter Baker Sports Centre, Wednesday night, when he lost consciousness.

“There were three people training for endurance diving. They were swimming slowly and trying to stay under as long as possible,” says JP Trottier of the Ottawa paramedic service. “They were not wearing any breathing apparatus.”

When the man was removed from the water he was not breathing and had no pulse. He was treated by lifeguards and paramedics before he was taken to hospital in critical condition.

Proponents of free-diving say people need proper training before attempting this activity.

Doug Sitter, president of Freedive Toronto, has been competing in the sport since 2001.

He says his longest dive is over 6-minutes without a breath.

“This is something that you need to do as part of a club environment with people who understand what the limits are and understand safety precautions so people don’t get into trouble,” says Sitter.

The city of Ottawa released this statement: "The City has a policy against sports and activities that involve holding one's breath underwater for prolonged periods of time.”

CTV's Natalie Pierosara will have more on this story tonight at six.